Principle of the sound level meter, rules for verification, and internal model structure analysis of associated models
Noise meter, also called sound level meter, is an instrument that can measure the noise level of industrial noise, domestic noise and traffic noise, etc., approximately according to the auditory characteristics of the human ear.
Noise level refers to the sound pressure level (dB) or loudness level (phon) measured with a sound level meter and corrected for hearing.
According to the accuracy of the sound level meter measuring 1000Hz pure tone under standard conditions, the international sound level meter was divided into two categories in the 1960s, one was called precision sound level meter, and the other was called ordinary sound level meter.
Our country also adopts this method. There are generally three types of noise weighting networks: A, B, and C. The A-weighted sound level is to simulate the frequency characteristics of the human ear to low-intensity noise below 55 decibels; the B-weighted sound level is to simulate the frequency characteristics of moderate-intensity noise between 55 and 85 decibels; the C-weighted sound level is to simulate the characteristics of high-intensity noise.
Since the 1970s, some countries have introduced a four-category method, which is divided into Type 0, Type 1, Type 2 and Type 3. Their accuracies are ±0.4dB, ±0.7dB, ±1.0dB, and ±1.5dB, respectively.
According to the different power sources used by the sound level meter, it can also be divided into AC type and DC type sound level meter with dry batteries, and the latter can also be portable. Portable has the advantages of small size, light weight and convenient on-site use.
Generally, it is composed of microphone, amplifier, attenuator, weighting network, detector, indicating meter and power supply.
(1) Microphone It is a device that converts a sound pressure signal into a voltage signal, also known as a microphone, and is a sensor. Common microphones are crystal, electret, moving coil, and condenser.
(2) Amplifiers and attenuators Many domestic and imported amplifiers that are popular at present use two-stage amplifiers in the amplification circuit, namely the input amplifier and the output amplifier, whose function is to amplify weak electrical signals.
(3) Weighting network Weighting network generally has three types: A, B, and C. The A-weighted sound level is to simulate the frequency characteristics of the human ear to low-intensity noise below 55 decibels; the B-weighted sound level is to simulate the frequency characteristics of moderate-intensity noise between 55 and 85 decibels; the C-weighted sound level is to simulate the characteristics of high-intensity noise.
(4) Geophone and indicator meter In order to display the amplified signal through the meter, a geophone is also needed to convert the rapidly changing voltage signal into a slower changing DC voltage signal.
